New exam content has to be integrated as a pretest question before it is operational; so yes, IFRS questions could become harder and more numerous as time goes on. This is from the AICPA:
The MCQs within each section are administered in three blocks, called “testlets.” Each testlet contains operational and pretest questions. Operational questions are scored, while pretest questions are not scored. Instead, a candidate’s response to a pretest question is used to evaluate the question’s statistical performance. It’s important to note that a majority of the questions are operational questions; however, pretest questions are mixed into the Exam and are not identified as pretest questions. From the candidate’s perspective, pretest questions are indistinguishable from operational questions. Pretest questions that meet certain statistical criteria are used as operational questions on future exams. This strategy for pretesting questions is common practice in high stakes testing.
There are three statistics used to describe the questions: Difficulty – whether the question is generally easier or more difficult for candidates, Discrimination – how well the question differentiates between more able and less able candidates, and Guessing – the chances of candidates answering the question correctly just by guessing. The statistics are generated when the questions are administered as pretest questions and used in the scoring when the questions are operational. The formulas for generating the statistics and scoring the Exam come from a scoring approach commonly referred to as “Item Response Theory.” Item Response Theory is currently being used or has recently been adopted by nearly all of the large licensing examination programs in this country and also by many of the moderate-sized and smaller examination programs.
Full version is here: http://www.aicpa.org/BecomeACPA/CPAExam/PsychometricsandScoring/ScoringInformation/DownloadableDocuments/How_the_CPA_Exam_is_Scored.pdf